HYDROGEN-BONDING OF AROMATIC-AMINES IN HYDROXYLIC SOLVENTS .1. ABSORPTION-SPECTROSCOPY OF SUBSTITUTED ANILINES AND HYDROGEN BOND-INDUCED REHYBRIDIZATION OF TRIVALENT NITROGEN-ATOMS

The longest wavelength absorption band of substituted anilines contain ing electron-accepting groups is characterized as an intramolecular ch arge-transfer (ICT) transition. Dual absorption peaks observed for the ICT transition of some para-substituted anilines in a strongly hydrog en-bonding solvent, hexafluoropropan-2-ol (HFP) can be attributed to t wo inequivalently hydrogen-bonded species with differently hybridized aniline nitrogens in HFP. The hydrogen bond-induced rehybridization ca uses appreciable changes in the ICT absorption spectra of highly polar aromatic amines. Rehybridization of aromatic amino nitrogens depends on the OH acidity in the solvent molecule and the basicity of the subs tituted anilines. The geometry of trivalent nitrogens in aryl amines i s critically dependent upon the ionization potential of the amino grou p, the electron affinity of the electron-accepting substituent and the substitution site of the electron-withdrawing group with respect to t he amino moiety.